1. Field of the Invention
The present invention relates to alkyltin thermal stabilizers for halogen-containing resin compositions. More particularly, the present invention relates to alkyltin sulfanyl diester thiols that have from one to three terminal thiol groups and are suitable for thermal stabilization of halogen-containing resins, e.g., PVC, compositions.
2. Description of Related Art
The conventional commercially available organotin stabilizers, such as alkyltin bis- and/or tris-(mercaptopropionates) and/or (thioglycolates) are prepared using thioacids (such as mercaptoacetic and mercaptopropionic), an aliphatic alcohol and mono- or di-alkyltin chloride, where all SH-group are reacted with the alkyltin chloride (alkyl groups are methyl, n-butyl or octyl). Alkyltin oxides (especially butyltin oxide) are also known to be used as a source of tin.
U.S. patent application Ser. No. 11/124,464, filed May 5, 2005, discloses an alkyltin compound of a specified formula that is said to have utility as a stabilizer for a halogen-containing resin. The alkyltin compound has from one to three terminal thiol groups. The heat stabilizing performances of dimethyltin bis(1,2-ethane dithioglycolate), monomethyltin tris(1,2-ethanedithioglycolate), dimethyltin bis(1,2-ethane dimercaptopropionate), monomethyltin tris(1,2-ethanedimercaptopropionate) and mixtures thereof are specifically disclosed.
U.S. Pat. No. 3,115,509 (see also GB 866,484) generically discloses condensation products of organotin compounds with dimercaptoacid esters of organic thiols. These condensation products have the general formulaRxSn(—S-A-COO—B—OOC-A-SH)4-x wherein x is 1, 2, or 3, R is a univalent organic radical, A is a hydrocarbon group, B is a hydrocarbon radical, and the sum of the carbon atoms of A and B is preferably no more than 25, and are said to stabilize vinyl resins against the degradative effects of both heat and light.
U.S. Pat. Nos. 3,539,529 and 3,682,992 disclose compositions and a stabilized polyvinyl chloride resin composition comprising essentially, in a predominant amount, a polyvinyl chloride resin and, in a small amount, at least one boron-containing organotin compound having the formula
wherein R is a member selected from the group consisting of alkyl, alkenyl, aralkyl, alkylaryl and aryl; X1 is a member selected from the group consisting of the residues of monomercapto compounds, dimercapto compounds and polymercapto compounds, said residues containing at least one free sulfhydryl radical; and X2 and X3 are members selected from the group consisting of hydroxyl, the same residues as X1, the residues of carboxylic acids and maleic acid monoesters, and the residues of mercapto compounds containing no free sulfhydryl radical.
The disclosures of the foregoing are incorporated herein by reference in their entirety.
Non-thiol terminated alkyltin stabilizers are also known. For example, dimethyltin bis S,S (2-ethylhexanol thioglycolate) and di-n-butyl bis S,S (2-ethylhexanol thiolglycolate) are both commercially available. One of the most effective thermal stabilizers is a blend of dimethyltin bis S,S (2-ethylhexanol thioglycolate) and methyltin tris S,S,S (2-ethylhexanol thioglycolate), which is also commercially available.